Aims: Pressure-controlled intermittent coronary sinus occlusion (PICSO) may improve myocardial perfusion after pPCI. We evaluated the safety and feasibility of PICSO after pPCI for STEMI, and explored its effects on infarct size and myocardial function. Methods and results: Thirty patients were enrolled following successful pPCI of a left anterior descending coronary artery culprit lesion for anterior STEMI, in whom PICSO for 90 minutes was attempted. Infarct size and myocardial function were assessed by cardiovascular magnetic resonance (CMR) at two to five days and four months post pPCI. An independent core laboratory selected matched historical control patients with CMR data for comparison. PICSO was initiated in 19 patients (63%), and could be maintained for 90 (±2) minutes in 12 patients (40%). Major adverse safety events occurred in one patient (3%). Comparing all PICSO-treated patients to matched controls demonstrated no significant differences in infarct size or myocardial recovery. However, infarct size reduction from two to five days to four months was greater for patients successfully treated with PICSO compared with matched controls (41.6±8.2% vs. 27.7±9.9%, respectively; p=0.04). Conclusions: PICSO is safe in the setting of STEMI, although feasibility was limited. Administration of sufficient PICSO therapy may be associated with enhanced myocardial recovery during follow-up, warranting further evaluation of this novel therapy.